Apparatus for spray coating articles in an electrostatic field



March 27, 1951 H. P. RANSBURG ET AL 2,546,701

APPARATUS FOR SPRAY COATING ARTICLES IN AN ELECTROSTATIC FIELD 2 Sheets-Sheet 1 Filed May 51, 1945 H Hm l March 27, 1951 H. P. RANSBURG ET AL 2,546,701

APPARATUS FOR SPRAY COATING ARTICLES IN AN ELECTROSTATIC FIELD Filed May 51, 1945 2 Sheets-Sheet 2 INVENTORS. law/V04 D kfl/vsa'ufis. ENER) MILLER.

Patented Mar. 27, 1951 APPARATUS FOR SPRAY COATING ARTI- CLES IN AN ELECTROSTATIC FIELD Harold P. Ransburg, Emery P. Miller, and Norman Curtis, Indianapolis, Ind., assignors, by mesne assignments, to Ransburg Electro-Coating Corp, Indianapolis, Ind., a corporation of Indiana Application May 31, 1945, Serial No. 596,870

Claims. 1

This invention relates to an apparatus for spray coating articles in an electrostatic field such as to electrically attract the coating material to the article or articles to be coated, and wherein the coating is discharged into such field for such purpose by a distributing agent such as a spray gun, reference being had to Letters Patent No. 2,247,963, granted July 1, 1941, upon an application filed by Harold P. Ransburg and Harry J. Green, entitled Apparatus for Spray Coating Articles. This application is a continuation in part of the copending application of Harold P. Ransburg, Emery P. Miller, and Norman S. Curtis, Serial No. 516,778 filed January 3, 1944, now abandoned.

An important object of this invention is to provide means for applying coating material to an article in an electrostatic field wherein the distributing agent of the coating material may be manipulated by an operator during the coating operation.

Another object is to permit the operator safely to adjust the discharge or precipitating electrode during the coating operation.

A further object of this invention is to provide safety equipment and control apparatus for hand spraying in an electrostatic field, wherein the spray gun may be grasped and manipulated by an operator to direct the spray over and about the article being coated while moving the gun to different positions relative thereto and over extended surfaces thereof.

Still another object of the invention is to so restrict movements of the gun (and of the discharge electrode where it is movable) that approach of the gun (or electrode) within sparking distance of an oppositely charged object will be prevented.

It is also an object of this invention to obtain manually controlled distribution of coating material in an electrostatic field and to protect the operator against hazards incident to such manual distribution while still providing an electrostatic field substantially equal in effectiveness to fields readily maintainable in apparatus wherein spray-nozzles are fixedly supported and it is unnecessary to guard against hazards incident to manual manipulation.

Such manual operation of the distributing agent by an operator, as distinguished from fixed agents or spray guns of the character disclosed in the above mentioned Letters Patent, is advantageous in the coating of articles of different sizes or configuration, or articles of peculiar or irregular shapes. Thus, under such conditions the position of the gun or electrode relative to the article, or the direction of the spray, may be changed according to the surface characteristics of the article or group of articles in the spray booth, and may be manipulated to properly coat 2 surfaces which a fixed gun could not adequately coat.

It is, therefore, the primary purpose of this invention to provide means whereby the manual operation of the spray gun by the operator will be permitted while spraying into an "effective electrostatic field. In this connection the prim cipal requirement is that of safety, since the voltage required is of such high potential as to make the manual operation of the spray gun extremely dangerous unless the operator is surrounded by adequate safeguards. It is also essential that provision be made to maintain a proper distance or gap between the discharge electrode and the article being coated, since they are of high potential difference. It is further desirable that the apparatus so maintain the juxtaposition of the gun and the electrode as to cause the spray to be discharged from without the electrostatic field, and where the gun and electrode may be of different potential, maintain sufficient gap between them for safety.

With this arrangement the flexibility of hand spray is combined with the economy of electro--- static coating, a highly desirable combination in the coatin of articles which are not repetitive in shape and color. Thus the human control is introduced into electrostatic coating wherein it may be difficult to coat articles by the fully automatic or fixed spray gun.

The various features of the invention, such as to obtain the above described advantages, will be more particularly set forth and described in the following specifications and accompanying drawings.

The full nature of the invention will be understood from the accompanying drawings and the following description and claims:

Fig. l is a perspective view of one formof apparatus embodying the invention.

Fig. 2 is a wiring diagram in connection with the apparatus of Fig. 1.

Fig. 3 is the same as Fig. 1 showing a modified form of the invention.

Fig. 4 is a wiring diagram of the apparatus shown in Fig. 3.

Fig. 5 is an illustrative view of a mounting for the spray gun and electrode of modified form.

Fig. 6 is the same as Fig. 5 showing a further modified form.

In the drawings there is illustrated electrostatic spray equipment including an overhead conveyor track I!) along which the carriers H are caused to slowly travel for conveying the articles 12, 12a to a position for establishing an electrostatic field for spray coating the surface thereof. Suitable means may be provided for slowly rotating the articles as they pass through the field where it may bedesired to spray coat the several surfaces thereof, such as bya rack bar l3 enga e ble b a pinion M on the carriers.

Adja ent to the line of travel of the articles and spaced therefrom there is an. adjustable protective structure for the operator indicated at 15, said structure including opposed fixed supporting elements I and an adiustable operating'frame IT. The operating frame iscarried on the horizontal supporting bars I 8 slidably s pported within the horizontal t bular bars of the elements I 6,

whereby the operating frame may be ad ustably positioned in predetermined spaced relation to the line of travel of the articles to be coated. The operating frame I! is provided with a pair of upright slide bars at opposite ends of the electrostatic field throughout which the operator may direct the spraying operation.

Slidably mounted upon the upri ht slide bars there is a horizontal control member 59 which carries with it, as that modification shown in Fig. 1, the forwardly extending insulating bars '20. Said bars carry on their forward ends the discharge electrode wires 2| which are'e ectrically connected to a source of hi h voltage '22 (Fig 2) through an insulated conductor 23 and a coil spring conductor 2 which insures electrical connection while the'electrode is moved to its various positions.

The manuallyoperated spray gun 25 is supported for universal movement on the control member H] by a ring 26 with which it is swivelly connected, whereby said gun may be manually directed in any direction and bodily moved lengthwise of the member I 9 within the structure, and further, whereby said gun is at all times restrained from too 'close an approach to the electrode. The gun is connected by suitable flexible hose in the usual manner to the supply of air and to the supply of coating material which in most instances, will be a liquid coating material such as paint.

The control member l9 has its weight counterbalanced by a suitable tension spring within the spring pulley 21 upon the structure 15 to which the member is connected by a pair of supporting cables 28. This permits the operator to readily and conveniently move this mamberAS with the gun up and down within the lower and upper confines of the operating frame l I on the supporting elements. The operating frame i! may also be preliminarily adjusted to position the electrode in proper spaced relation to the line of travel of the articles and there locked by the lock screws 29. Thus, where the adjacent side of the articles to be coated move along the same plane, the operator is assured that the spacing between the articles and the electrode will be correctly maintained, while he will be permitted to direct the spray in any direction and move the gun laterally or vertically to cover the full surface of the articles. Where the surface of the articles conveyed through the field may vary within limits, the set screws 29 may be freed and a stop collar 3 may be secured to the supporting bar l8 between the supporting element l6 and a limit bracket 3] to limit movement of the frame ll. This will permit the operator to move the electrode 2! toward and away from the articles within safe limits to maintain proper spacing between. the electrode and the articles passing through the field.

In those instances where an article to be coated is of such shape or contour as to present a projection or surface which will project dangerously or undesirably close to the electrode, means are provided for automatically rendering the apparatus inoperable.

4 This means as shown herein comprises a photo-electric cell 33 and a light source 32 carried by the frame H and so spaced relative to the electrode that the actuating light beam will be interrupted when an article would approach so close to the electrode as to cause a spark therebetween.

As shown in Figs. 2 and 4, the photo-electric cell actuates a switch 35 in a control circuit concontrols the source of high voltage. Thus there 7 is shown an arrangement for rendering the apparatus inoperable to preclude the possibility of a spark. Similar inoperability could be attained bystopping the conveyor or by simultaneously deenergizing the voltage source and stopping the conveyor whichever appears most desirable. The operator may thereby be assured that if some article comes along the conveyor, such as to too closely approach the plane of the electrode, the circuit therethrough will be broken. I

To insure the opening of the central circuit should the operatorleave his position, and to permit him to quickly and conveniently open the circuit through the electrode if any difficulty arises, there is provided a hand-pull switch cord 34 which he must grasp with his free hand and pull down in order to close the normally open circuit control switch 35. Upon his release of the pull cord, the circuit through the electrode will be broken.

In the modification shown in Fig. 1 and Fig. 2, the operator, structure, articles to be coated, and spray gun are grounded, and when the circuit is closed the electrode is at high potential. When the photo-electric barrier relay 3%, the pull cord switch 35, and the switch 3'? on the spray gun are all closed, volts will be supplied from the line 38 through the control circuit to the control relay 39. The relay 39, upon thus being closed, energizes the primary circuit of the high voltage source 22 with 220 volts from the power line 38a. This in turn induces voltage in the secondary circuit of the high voltage trans former composed in series of ground it. transformer secondary coils 4!, and rectifying tube 42. This causes high voltage current to pass through the connector line 23, spring 25, electrode 2 l, and thus establishes the field between the articles l2 and IM and the electrode 2|, the circuit being completed by Way of the articles, conveyor track it and ground 43. The coating material for precipitation upon the item is sprayed into this field by the operator l5 as he manipulates the gun 25. I

In the above described modification of the invention the operator and the gun are grounded, whereas the electrode is charged at high voltage. Another modification may be provided wherein the operator and spray gun, or equivalent means of introducing small particles of the material to the forces of the field, are of high potential. In this case, there is mounted on the gun an electrode [2! (Fig. 3) which effectively ionizes the particles of coating material in the jet and efiects their precipitation on the article. In this arrangement, because of the field which exists between the charged gun and the article, the foremost portion of the gun also acts as a discharge electrode. Such an arrangement is illustrated in Figs. 3 and 4, in which parts previously described are represented by like numbers. The electrode l2l, which permits the eliminationof the electrode supports 2% and electrode 2! of Figs. 1 and 2, is in the form of a fine wire supported from the gun 25 in advance of the discharge end of the gun and in position to surround thejet discharged therefrom.

The electrical connections in the apparatus of Fig. 3 are shown in Fig. 4, from which it will be apparent that, in contradistinction to the apparatus of Figs. 1 and 2, the spray gun 25 and discharge electrode IZI are rigid with each other instead of being capable of relative movement; and the spray gun, the discharge electrode, the operator, and the entire protective structure including an operator's platform are insulated from ground and maintained at a high electrical potential relative thereto. To prevent any possibility of feed-back of high voltage to the supply line, low voltage circuits leading to or from the operators platform or apparatus supported thereon may include one-to-one insulated transformers, as shown.

' The protective structure including the control member I9 prevents the electrode, as it is moved parallel to or shifted to different positions and angles with respect to the articles, from approachi'ng too closely to the articles. However, the plane of movement of the gun and electrode may be adjusted with respect to the plane of travel of the articles by the adjustment of the operatingframe I! in respect to the fixed supporting elements I6 in the manner before mentioned.

In order that the operator will be protected from being grounded while at such high potential, a switch control plate I22 is provided upon which he must stand in order to close the circuit during operation. In this modification, the plate I22 is mounted upon a supporting platform I23 upon which the supporting elements I6, operating frame I? and its control member I9 are also mounted. The platform and the elements supported thereon are insulated from ground by insulator legs I 24. Since the edges of platform I 23 substantially overbou-nd. the edges of plate I22, it is necessary for the operator to remove himself from within the confines of plate I22 before he can step to ground. Therefore, immediately upon removal of the operator from the switch control plate I22, the switch is opened and the operator may descend from the platform I23 to ground with utmost safety. Also, in this arrangement it is required that the supply tube I26 from the air source shall not provide an electrical path to ground. Therefore, the flexible tubing to the gun is directly connected with a tank I25 which contains a coating material, said tank being supported upon the insula ed platform Iii-3. and only connected with a source field is produced in the space between the electrode I21 and the articles to be coated. However, the operator cannot leave the platform without breaking the circuit through one or more of the. several switches 35,, 31. or I22, and he cannotv ground himself while. in position to close said switches.

I As shown in Fig. 5, the control member is carrying the gun 25 and the electrode i ZI thereon, as in Fig. 3, may be mounted to slide up and down. upon a curved operating frame M3. or, as shown. in Fig. 6, a semi-circular operating frame 3 I 1 may be employed about which the sun and electrode may move. The curved or semi.- oircular operating frames may be in the form of attachments to be secured to the straight upright portions of operating frame I1 of Figs. 1 and 3,. With such arrangement, either the electrode I2I carried on the gun at high potential or the electrode 21 carried by insulating bars 20 upon the control member I9, may be used.

By means of, the curved or semi-circular operating-frame, the operator may more conveniently move the gun and electrode into position for coating the upper or lower ends or surfaces of the articles in the spray zone.

The articles to be coated are herein shown as in effect comprising a collecting electrode or terminal for the circuit including the source of high voltage for producing a high. potential difference between the discharge electrode and the articles. Where such articles may be of nonconductive material, they may be mountd on or supported by a metal conductor, which, in effect, results in the high potential difference being produced between the discharge electrode and the non-conducting article. For that purpose such article-support is herein considered to constitute a part of the article during its passage through the spray zone.

Also, whereas the invention in its several modifications. has been described in detail for illustrative purposes, it is to be understood that the circuit may be revised. so that the discharge electrode is grounded and the articles or their supports comprise a collecting electrode at high electric potential, or so that the. discharge electrode and, the articles to be coated ortheir supports are each at a high electric potential of different polarity.

The electrodes 2 I and I2 iof both modifications shown re desirably formed of relatively fine wire, preferably wire. in the neighborhood of .010 inch in diameter when the high voltage em ployed is in the neighborhood of 100,000 volts. The electrode in each apparatus not only serves in the maintenance of an effective electrostatic field between it and the articles tobe coated, but also, because of the small diameter of the wire composing it and the manner of its mounting, creates a movable corona discharge which very effectively ionizes and tends to confine the coating-material particles.

In both modifications the gun and the operator are at the same potential. This makes it possible for the operator to grasp the gun directly and manipulate it. with greater facility and accuracy than if it were necessary to interpose sufiicient insulation to. protect the operator from the volttrode and located closer thereto than are the articles to be coated. This is an advantage, as the presence of any such parts could interfere seriously with the maintenance of an effective '15 field. between the electrode and the articles.

Parts of the above disclosure which have not been claimed herein are the subject of the patent applications of Harold P. Ransburg, Serial Nos. 208,140 and 210,743 filed January 27, 1951 and February 13, 1951 respectively.

We claim as our invention:

1. Apparatus for spray coating the surface of an article in an electrostatic field, comprising a sup-port for the article, a movable spraying device for creating a spray of atomized coating material directed generally forwardly toward an article on said support, said spraying device having a discharge electrode at its forward end, means including a source of high voltage for maintaining between said electrode and the article on said support an electrostatic field promcting the deposition on the article of the atomized coating material constituting said spray, said spraying device being provided with a handle which is spaced rearwardly from the electrode so that an operator grasping said handle can manipulate the spraying device from without said electrostatic field, means located rearwardly of said electrode and operatively connected to said spraying device at a point thereon in rear of the electrode for guiding said spraying device for movement in and for confining such device to a zone extending generally parallel to and spaced from the surface of the article, and a support for said guiding means operative to limit the approach to the article of both the guiding means and the spraying device connected thereto.

2. Apparatus for spray coating a series of 'articles, comprising a conveyor for moving the articles successively over a predetermined path through a coating zone, a movable spraying device for creating a spray of atomized coating material directed generally forwardly toward the article-path, said spraying device having a discharge electrode at its forward end, means including a source of high voltage for maintaining between said electrode and the articles an electrostatic field promoting the deposition on the articles of the atomized coating material constituting said spray, said spraying device being provided with a handle which is spaced rearwardly from the electrode so that an operator grasping said handle can manipulate the spraying device from without said electrostatic field, means located rearwardly of said electrode and operatively connected to said spraying device at a point thereon in rear of the electrode for guiding said spraying device for movement in and for confining such device to a zone extending generally parallel to and spaced from the articlepath, and a support for said guiding means operative'to limit the approach to the article-path of both the guiding means and the spraying device connected thereto.

3. Apparatus for spray coating the surface of an article in an electrostatic field, comprising a movable spraying device for creating a spray of atomized coating material directed generally forwardly toward the article to be coated, said spraying device having a discharge electrode at its forward end, means including a source of high voltage for maintaining between said electrode and the article an electrostatic field promoting the deposition on the article of the atomized coating material constituting said spray, said spraying device being provided with a handle which is spaced rearwardly from the electrode so that an operator grasping said handle can manipulate the spraying device from without said electrostatic field, means operatively connected to said spraying device for confining it to movement in a zone spaced at a predetermined minimum distance from the article, and control mechanism for said field-maintaining means, said control mechanism including a switch hav ing an operating member associated with said handle, biased toward a controlling position in which it renders the field-maintaining means inoperative, and movable by the hand of the operator into a second controlling position permitting operation of the field-maintaining means.

4. Apparatus as set forth in claim 3 with the addition that said control mechanism includes a second switch having an operating member remote from the field between the electrode and article and controllable by the other hand of the operator, biased to one controlling position in which it renders the field-creating means inoperative, and manually movable to a second controlling position in which it permits operation of such means.

5. Apparatus for spray coating an article in an electrostatic field, comprising a protective structure adjacent but spaced from the article to be coated, said structure providing an operators station and limiting approach tothemticle of an operator at said station, a movable spraying device for creating a spray of atomized coating material directed generally forwardly toward the article, means operatively connecting said spraying device to said protective structure and confining the spraying device to movement in a zone spaced at a predetermined minimum distance from the article, said spraying device projecting through said protective structure and having a discharge electrode on the article side of such structure and a handle on the operator's side of the structure, and means including a source of high voltage for creating a high potential difference between said article on the one hand and said electrode and protective structure on the other hand whereby to maintain between the electrode and article an electrostatic field promoting the deposition on the article of the atomized coating material constituting said spray.

HAROLD P. RANSBURG. EMERY P. MILLER. NORMAN CURTIS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,855,869 Pugh Apr. 26, 1932 1,910,674 Bramsen et al. May 23, 1933 1,919,798 MacLaurin July 25, 1933 2,097,233 Meston Oct. 26, 1937 2,128,327 Russell et a1 Aug. 30, 1938 2,152,077 Meston et a1. Mar. 28, 1939 2,173,032 Wintermute Sept. 12, 1939 2,174,328 Meston et al. Sept. 26, 1939 2,247,963 Ransburg et a1. July 1, 1941 2,270,341 Ransburg Jan. 20, 1942 2,274,726 Melton Mar. 3, 1942 2,302,185 Campbell Nov. 17, 1942 2,302,289 Branstrom-Cook Nov. 17, 1942 2,404,454 Owens July 23, 1,946 2,417,798 Ransburg et a1. Mar. 18, 1947 FOREIGN PATENTS Number Country Date 591,474 Great Britain Aug. 19, 194'? 

